1. Field of the Invention
The present invention relates to a voltage fluctuation compensating apparatus for detecting and compensating a voltage dip when voltage of an electric power system supplied to a load dips instantaneously.
2. Description of the Related Art
In some cases, voltage of an electric power system may dip instantaneously due to lightning so that a precision machine in a factory malfunctions or stops temporarily to cause great damage in a production line. In order to prevent such damage, there is used a voltage fluctuation compensating apparatus for monitoring voltage fluctuation such as an instantaneous voltage dip in an electric power system, and compensating the voltage dip.
FIG. 18 is a schematic configuration diagram showing a related-art voltage fluctuation compensating apparatus. As shown in FIG. 18, electric power from a power line 1 is stepped down by a transformer 2, and then connected to a customer 3 (load) through a voltage fluctuation compensating apparatus. Thus, electric power is supplied to the customer 3. The voltage fluctuation compensating apparatus includes a DC power source 4, an inverter 5, a smoothing filter 6, and a high-capacity transformer 7.
Description will be made below about the voltage compensating operation in such a related-art voltage fluctuation compensating apparatus at the time of an instantaneous dip of a system voltage.
FIG. 19 shows a system voltage, an output of a voltage fluctuation compensating circuit, and a voltage supplied to the customer 3, respectively, at the time of an instantaneous dip of a system voltage. As shown in FIG. 19, when a voltage dip occurs instantaneously in the system voltage, the voltage dip is detected by a detection unit (not shown) which monitors voltage fluctuation. By the power feeding control based on the detected voltage dip, an AC voltage is generated by the DC power source 4 and the inverter 5 in the voltage fluctuation compensating apparatus. The AC voltage is connected in series to the power system through the smoothing filter 6 and the high-capacity transformer 7. Thus, the voltage dip of the power system is compensated. As a result, the output voltage from the voltage fluctuation compensating apparatus is added to the system voltage in which the voltage dip has occurred, so that electric power with a normal voltage is supplied to the customer 3.
Since the related-art voltage fluctuation compensating apparatus is configured thus, the system voltage flows into the inverter 5 through the transformer 7 correspondingly to a load current even when the system voltage is normal. As a result, loss by the transformer 7 and the inverter 5 occurs even at the normal time. Thus, a large-scale cooling unit is required.
In addition, since a voltage is supplied to the power system through the smoothing filter 6 and the transformer 7 at the time of an instantaneous dip of the system voltage, the capacities of the smoothing filter 6 and the transformer 7 becomes high. Thus, there has been a problem that the apparatus increases in size.